Correlations Between Environmental Factors and Increasing Lyme Disease Incidence in Canada

Abstract

BackgroundLyme disease (LD) is an emerging infectious disease in Canada due to northward expansion of the geographic range of Ixodes scapularis, the principal tick vector for the LD agent Borrelia burgdorferi, into central and eastern Canada. This study aims to i) summarize the surveillance data for LD cases reported in Canada between 2009 and 2015, ii) identify potential environmental risk factors and iii) develop an acarological risk indicator from passive surveillance for occurrence of human cases.MethodsWe described the distribution, trends, demographic and clinical characteristics of cases of the disease. Logistic regression models were used to identify risk factors for the occurrence of LD: 1) demographic (age and sex), and 2) environmental (type of forest cover, temperature and abundance of ticks). Passive surveillance data were used to develop an acarological indicator of at-risk areas for LD.ResultsThe number of reported LD cases increased more than six-fold overall, from 144 cases in 2009 to 917 cases in 2015, mainly due to locally acquired infections. LD incidence in Nova Scotia has risen sharply since 2013 and was the highest in Canada over the study period. Children below 15 years and adults of the 55–74 age groups reported highest incidence. Significantly more men than women were infected and men had significantly more symptoms of late disseminated LD than women. Variability in clinical manifestations is observed between provinces, years, for children below 15 years and between age groups. The majority of cases were reported between April and November and there was an increase in risk areas. The abundance of Ixodes scapularis ticks collected on humans and deciduous forest cover were significantly associated with the occurrence of LD cases at the municipality scale. Passive surveillance provides a cost-effective alert tool for public health authorities to timely identify risk areas and target vulnerable populations and front-line health professionals by means of awareness campaigns.ConclusionThese findings showed that LD continues to increase in Canada, both over time and geographically, underlining the need to implement better preventive strategies, early disease recognition and treatment and efficient surveillance systems.Disclosures All authors: No reported disclosures.